Burner control system



Aug. 13, 1946. P. ARANT BURNER CONTROL SYSTEM Filed Sept. 24, 1941 2 m M M m 1% W 5 r a fl F a M 5 U r ,T L r 6 H on m 9 w 5 a, 5 a 6 M up a M 0 7 3 z .9 a W m #4 a L n v? w z 4 .m MW m 9 3 5 6 Q .7 4 02 MM 6 I Tva 2 J w/ 9 M 7 P 8 v u 6 Z n q w 6 55 L W I 3.. w w 11% Q 0 2 wk 4 w "luv u 7 i A J w n a m P. a fi @3 w T F Patented Aug. 13, 1946 UNITED STATES PATENT OFFICE BURNER CONTROL SYSTEM Perry Arant, Alhambra, Calif., assignor to Clayton Manufacturing Company, Alhambra, Calif.

Application September 24, 1941, Serial No. 412,193

26 Claims. 1

This invention relates to control means for fuel burners of the atomizing type and more particularly to a control system for a burner whose fuel is electrically ignited.

More specifically, the invention relates to a control system for spark-i nited burners which will avoid all danger of explosion or fire.

Nearly all explosions in burner operating with atomized fuel are the direct result of ignition failures, either momentary or complete. Ignition failures may be the direct result of improper setting of the spark gap, carbonizing of one or both of the electrodes, a cracked electrode permitting partial short circuiting, a wet or moist high tension wire, etc. Momentary ignition failures are dangerous because they usually occur after the fuel has been sprayed into the combustion chamber, thereby forming an explosive mixture which is ignited upon recurrence of the spark, In some instances, especially with partial short circuiting due to moisture, the heat of the spark will dry out the moisture quickly, permitting a delayed spark at the time the combustion chamber is full of vaporized fuel. Complete spark failure ma be dangerous if it occurs at a time when the walls of the combustion chamber are still hot, or when a piece of glowing carbon remains in the combustion chamber, and fuel is supplied t the burner. This source of danger presents itself when an attempt is made to start the burner immediately after having been cut off and the spark completely fails, but the combustion chamber is still hot enough to cause the fuel to flash.

The principal object of the invention is to provide a control system for a burner which will positively prevent explosions and eliminate the danger and/or injury which usually result therefrom.

Another object of the invention is to provide a control system which will prevent fuel from being introduced into the combustion chamber when said chamber is in a hot condition.

Another object of the invention is to provide a burner control system which will scavenge the combustion chamber of combustible gases before fresh fuel can be introduced thereinto.

Still another object of the invention is to provide a burner control system which will prevent fuel from being supplied to the burner except when the ignition spark is of sufficient intensity to ignite the fuel.

A further object of the invention is to provide a burner control system for general use with oil or gas furnaces, or furnaces burning highly volatile fuel such as high octan gasoline which produces a particularly hazardous explosive mixture.

A still further object of the invention is to provide either manual orfully automatic control means for a fuel burner which is easy to install, relatively inexpensive, and above all dependable and fool-proof.

In brief, the present invention comprises a control system having a bi-metallic electrode or thermostat-electrode arranged so that it serves as one of the spark electrodes and is initially subjected to the heat produced by a high voltage spark. In standard oil burner installations the ignition transformer usuall has an output of about 10,000 volts at 23 milliamperes. A drop of as little as 1500 volts in this output due either to a resistance which may be caused by a partial short circuiting or by a line-voltage drop would prevent the bi-metallic or thermostat element from expanding to the extent desired even though it be continuously subjected to the heat of the spark for an hour. Carbon on the tip of the electrodes is another common fault and if this occurs to the extent that a 25% reduction in the proper spacing of the electrodes is made, the spark gap will give off insufiicient heat to actuate th thermostat.

A push rod is associated with the thermostat element and is arranged t actuate an ignition switch and a fuel control switch upon expansion of said thermostat. These switches are of the mercury type and the ignition switch may be considered a break switch since it produces a break in the circuit upon being actuated, and the fuel control switch may be considered a makef switch since it makes or completes a circuit to a solenoidoperated fuel control valve upon being actuated. These switches are associated with a double-pole relay and an ignition transformer and are arranged in a circuit so that upon the closing of a main switch, either manually or automatically, a circuit to the spark electrodes will be completed and sparking will commence. This spark heats the bi-metallic electrode and the arrangement is such that if said spark is of sufficient intensity to ignite the fuel it actuates the thermostat-electrode, whereby the fuel control switch is made and fuel is allowed to flow to the burner nozzle. After fuel ignition has occurred, the thermostat is further expanded by the heat of combustion of the fuel to break or open the ignition switch. The circuit is such, however, that current continues to be supplied to the electrodes so long as the main switch is closed.

If the spark gap, for any reason, fails to pro- 3 duce the heat necessary to actuate the thermostat-electrode, no fuel whatever will be supp to the burner and hence there is eliminated not only the danger of explosion but the fire hazard which would result from the introduction of fuel into the combustion chamber.

Once the ignition switch has been opened and the current to the relay has been cut off, as by opening of the main switch, no spark can be produced until the thermostat-electrode has had an opportunity to cool and contract and thereby allow the fuel control switch to resume its initial break position and for the ignition control switch to assume its original make position, in the order named. Accordingly, one of the important features of the present invention is the inclusion of a dual-purpose blower, which blows air through the fire box or combustion chamber to expel any explosive vapors therefrom and also cools the thermostat-electrode, as prerequisites, before the supply andignition of fuel can take place. In this'connection, the push rod is made hollow and provided with a plurality of apertures which conduct -a stream of air-to the inner surface of the thermostat-electrode to-assist in cooling the inner surface of'the same. In-practice, in a particular steam generating unit, the fire box or combustion chamber can be cooled down in about 45 seconds from a red hot condition to a cool condition such that the thermostat-electrode will be substantially completely contracted to a condition comparable to that which it is in at a cold start. Once the thermostat has been cooled, or where the furnace is started from 'a cold condition, only about six seconds time is required for the spark to heat and actuate the thermostat-electrode. When the furnace is started from a cold condition, this six seconds delay provides ample time for the blower to scavenge the fire box or combustion chamber of any combustible gases that may haveremained therein. At the same time, the cooling effect on the thermostat-electrode is insufficient to prevent said electrode from being heated by the spark, once the spark has been initiated.

One of the important safety features of the present control system is a holding circuit which maintains the relay closed so that an ignition spark is provided during the entire period of operation of the burner, notwithstanding that the ignition switch is caused to break after the fuel has been ignited. This ignition switch remains broken or open until the thermostat electrode cools, and is so associated with the relay that said relay cannot be energized to restore the spark unless said ignition switch has first been allowed to make.

Other objects and features of the invention will be apparent from the following description taken in connection with the accompanying drawing in which:

Fig. 1 is a diagrammatic View of a control system embodying the principles of the present invention;

Fig. 2 is an enlarged detail view of the means associated with the thermostat-electrode for varying the relative time of actuation of the ignition switch and the fuel control switch;

Fig. 3 is a fragment of a system like that shown in Fig. 1 but including a switch responsive to the pressure in the fuel line and arranged so as to out on current to the system in event'of fuel failure; and

Fig. 4 showsafragment of a modified circuit in which the ignition is cut off after the fuel has been ignited.

Referring to Fig. l, the numeral 5 indicates a gasoline engine which is connected by a coupling 6 with a generator I capable of supplying any suitable alternating current, for example, volts A. C. at 60 cycles. Current from the genorator l is carried by the lines 8 and 9, respectively. A main switch It is associated with the lines 8 and 9 and controls the flow of current from the generator to the remainder of the apparatus. The switch l0 may be a manually actuated switch or a thermally responsive switch depending upon whether a manual or automatic control is desired.

While a gasoline engine and generator have been illustrated for supplying current to the control system, it will be understood that such current may be derived from any other suitable or convenient source.

The lines 8 and 9 are connected with an electric motor H which is placed in operation whenever the main switch It is closed. The motor H is preferably arranged to simultaneously drive a blower l2 and a fuel pump l3, a belt l4 being employed for this purpose. The blower I2 is arranged to deliver air to a burner air-intake chamber [5, which may be plain or of the volute or spiral flow type, and the fuel pump 13 is arranged to supply fuel to a burner nozzle it through a. conduit I1 under the control of an electrically operated valve, such as a solenoid actuated valve l8, as will be explained more fully hereinafter. A conduit I9 connects the fuel pump 13 with a suitable source of supply.

In the event that the present control system is used with a gas burner, it will be apparent that the fuel pump l3 may be omitted and the valve l8 utilized to control the supply of fuel to the burner.

Anelectrode 29 is disposed in the chamber l5 adjacent to the burner nozzle H3. The electrode 20 is connected by a high tension cable 2| with the secondary coil 22 of a conventional ignition transformer 22. The coil 22 is grounded, as indicated at 23. A second electrode 24, in the form of a bi-metallic strip or thermostat element, is disposed in spaced cooperating relation with the electrode 26 and is generally U-shaped. One leg 25 of the thermostat-electrode 24 is suitably fixed adjacent the burner nozzle Hi and is grounded as indicated at 26. A double-pole relay switch 2! is provided for controlling the ignition and supply of fuel in conjunction with an ignition control mercury switch 28 and a fuel-control mercury switchZS. Current is carried from the'line 9 to the relay switch 21 through a conductor 30. A conductor '3l connects the conductor 3il'with a contact R of the relay 21. Current from the line 8 is carried by a conductor 32 to one end of the primary coil 22 of the ignition transformer 22. The opposite end of said primary coil is connected by a conductor 33 with a contact R. of the relay switch 21, which cooperates with the contact R.

The ignition switch 28 is, for the purposes of the present invention, pivotally mounted, as indicated at 35. This switch is arranged so that when the burner is cold it is made, or, in other words, the mercury in the switch completes a circuit between its two contacts 36 and 31. The contact 36 is connected by a conductor 33 with'a contact P of the relay 2! and with the relay coil itself. On the other hand, the contact 31 is connected by aconductor '39-with a contact P 'ofthe relay 21, and by a conductor 39' with the conductor 32 going from the line 8 to one end of the primary coil 22 of the ignition transformer 22.

The fuel control switch 29 is similar to the ignition switch 28 and is pivoted at A!) but is arranged so that it is open when the bi-metallic electrode .25 is in the cool condition. Thatis to say, the mercury in the switch 29 is at the end remote from contacts 4H and 42. The contact 4| is connected by a conductor 23 with the conductor 39 and the contact 42 is connected by a conductor 44 to one side of a signal lamp 45 and to one terminal it of the solenoid-operated fuel flow control valve :8. The other terminal 21 of the solenoid Valve l 8 is connected by a conductor 48 with theopposite side of the signal lamp 45 and with the conductor 33 going to the contact R of the relay 27.

The ignition switch 28 and the fuel control switch 29 are actuated through a hollow push rod 49 associated with the free leg 55 of the bi-metallic electrode 24. One end 5| of the rod 49 is engaged with the leg 58 of the thermostat and the opposite end of said hollow rod is received in a block 52 slidably mounted upon a base 53. The rod 39 extends through a support 54 secured to the base 53 and carries a nut 55. A light compression spring 56 is mounted upon the rod 49 between the support 54 and the nut 55 and continuously tends to urge the rod 39 toward the right into engagement with the leg 55 of the bi-metallic electrode or thermostat 24. The pressure exerted by the spring 56 can be varied by suitable adjustment of the nut 55 to vary the travel of the slidable block 52.

The block 52 slidably receives one end 5? of a rod 58 adapted to effect actuation of the ignition switch 28 to break or open the same before the burner has been ignited, the spark circuit being maintained after initiation through the switch 28 by the relay 2?, as will be pointed out later. The rod 58 has a squared end 59 abutting a rod 60 operatively associated with an arm 6| which may form a part of the cradle for the ignition switch 23. The rod 58 is threaded and carries an adjusting nut 62 and a spring 63 is mounted on said rod between the adjusting nut 62 and the end 5?, whereby the tension of the spring 63 may be varied to alter the time of cutout of the ignition switch .28. It will be apparent from the foregoing that expansion of the thermostat-electrode 24, or, in other words, a movement of the thermostat leg 59 toward the left, as viewed in Fig. 1, will exert a force upon the push rod 49 tending to slide the block 52 toward the left. The block 52 in turn tends to move the rod 58 along with it through the intermediary of the spring 63. Movement of the rod 58 in turn effects corresponding movement of the rod 61] with the result that the ignition switch 28 is tilted on its pivot 35 to break the circuit through this switch to the ignition transformer 22.

The fuel control switch 29 is similarly actuated by the slide 52 through a rod 64 carrying an adjustable nut 65 and a tensioning spring 66. The rod 64 abuts one end of a rod 67 associated with an arm 58 which may form a part of the cradle carrying the fuel control switch 29. As has been previously indicated, the fuel switch 29 is arranged so that it is normally open but closes upon actuation or tilting. It will be apparent that movement of the block 52 will effect the desired tilting of the fuel control switch 29 so that the circuit to the solenoid valve I5 will be completed to efiec't opening of said valve and permit fuel to be pumped to the burner nozzle H5.

The relative timing of the operation of the ignition switch 28 and the fuel control switch 25 may be varied by adjusting the tension of the springs 63 and 66 through the nuts 62 and 65, respectively. Preferably these switches are so timed that the ignition switch 28 opens or breaks before the fuel switch 29 closes or makes. Opening of the ignition switch 28 does not interrupt the spark because the relay 2'! maintains the ignition circuit, as will be explained more fully hereinafter.

After the burner has been out off by either manual or automatic opening of the main switch It, the thermostat-electrode 24 will begin to cool and contract permitting the spring 56 to return the push rod 49 and slidable block 52 to their initial position. Any suitable means, such as spring or counterweights (not shown) may be provided to effect the return of the mercury switches 28 and 29 to their original positions of make and break, respectively.

The positioning of the thermostat-electrode 24 in relation to the air stream introduced by the blower i2 and with respect to the combustion chamber w is quite important inasmuch as this element must be so placed and shielded that the incoming air is incapable of preventing said thermostat-electrode from bein heated by the spark to actuate the ignition switch 28 and the fuel flow control switch 29.

In accordance with the present construction, the upper portion of the bimetallic electrode 24 is exposed to some extent to the incoming air and to the heat reflected from the combustion chamber 1 5. However, the electrode 24' is other-' wise protected from incoming cool air by a shield in which prevents the incoming air from directly acting upon the inner surface thereof. However, in order to control the cooling action of the thermostat-electrode 24, as when it is desired to start the furnace when in a hot condition, the hollow push rod 49 is provided with apertures or holes H which communicate with the air-intake chamber l5. These holes face the oncoming air stream and serve to conduct a portion of said air to the underside of the lei-metallic electrode 2 5 to thereby cool the same.

In an operative embodiment of the invention the thermostat-electrode is completely heated from a cold start in about six seconds, and cooled down from a red hot fire box condition in about 45 seconds. These time periods will, of course,

vary with the size of the apparatus, the relative I amount of fuel burned, etc. The timing is also affected by the distance of the reflecting walls of the fire box from the burner nozzle, etc.

The operation of the device is as follows:

Assuming that the furnace is in a cold condition, the thermostat-electrode 24 will be contracted so that it preferably exerts no force whatever upon either the ignition switch 28 or the fuel control switch 29 through the push rod 49. Hence, the ignition switch 28 remains closed and the fuel flow control switch 29 remains open. So long as the main switch I 0 is open,v

the relay 2! is de-energized and all of the contacts thereof are open. However, when the main switch If! is closed, either manually or automatically, the motor ll starts driving the blower I2 and the oil pump I3. Air is blown into and through the air chamber 15 and the combustion chamber 15 but no fuel is delivered to the burner nozzle 16 because the solenoid valve I8 is now 7 closed. The fuel pump I3 is preferably arranged so as to by-pass fuel to avoid building up excessive pressure in the pump or line [1 until such time as the solenoid valve 18 is opened.

When themain switch is closed, the ignition switch 28 already being closed, the relay 21 is energized by a circuit which may be traced from the line 8 through conductors 32, 39' and 39, across contacts 36 and 31 of the ignition switch 28, conductor 33, relay 21 and conductor 30 to the other side of the line 9. This energization of the relay 21 closes the contacts P and P to complete a holding circuit for the relay which can be traced from the line 8 through conductors 32, 39 and 39 to the contacts P and P, through conductor 38 to the relay 21, and from the relay 21 through conductor 33 back to the line 9. In other words, the contacts P and P are in parallel with the ignition switch 28 and subsequent opening of said ignition switch upon spark-heating and expansion of the thermostat-electrode 24 will not tie-energize the relay 21.

Energization of the relay 21 also closes the contacts R. and R to complete a circuit through the primary coil 22 of the ignition transformer 22. The primary circuit for the ignition transformer 22 may be traced from the line 8 through the conductor 32, the primary coil 22*, conductor 33 to the contact R. and from the contact R through the conductors 31 and 33 back to the other side of the line 9. of the ignition transfer 22 can be traced from the ground connection 23 through the secondary coil 22* of the ignition transformer 22, conductor 2i, electrode 20, the thermostat-electrode 24 to the ground connection 26, whereby an ignition spark is established between the plain electrode 29 and the thermostat-electrode 24. Inasmuch as the fuel switch 29 is open at this time, the solenoid valve I8 is not energized and therefore remains closed. The ignition spark between the electrode 26 and the thermostat-electrode 24 heats said thermostat-electrode and causes it to expand. When the thermostat-electrode 24 reaches a predetermined temperature it will have expanded sufficiently to actuate the ignition switch'28 to break the circuit at the contacts 36 and 31, actuation of said ignition switch being effected through the push rod 49, block 52, spring .63 and rods 53 and 60. This does not interrupt the spark because the ignition circuit is now maintained by the holding circuit previously described. Further expansion of the thermostatelectrode 24 will actuate the fuel control switch 29 through the push rod 49, spring '66, and rods 34 and 161 to effect closing of this switch and completion of the circuit to the solenoid valve 18, which circuit can be traced as follows: From line 8 through conductors 32, 39', 39, 43, across the contacts 4! and 42 of the fuel control switch 29, conductor 44 to one terminal 46 of the solenoid valve 18 and from the other terminal 41 of said solenoid valve through conductors Miami 33, through contacts R and R of the relay 21 and through conductors 3| and 30 back to the other side of the line 9. Completion of this circuit effects opening of the solenoid valve l8 and allows the fuel pump l3 to supply oil to the burner'nozzle 16. As has been previously stated, if the spark between the electrodes 29 and 24 fails altogether, or fails to reach a predetermined intensity or temperature sufficient to ignite the fuel,- the fuel switch 29 will not be actuated and the-circuitto the solenoid valve 18 will not be completed. However, completion of the circuit The secondary circuit 8' V to the solenoid valve 18 also completes the oilcuit to the signal lamp 45 which is then illuminated to indicate that fuel is being supplied to the burner nozzle it.

When the main switch I0 is opened, either manually or automatically, to shut down the burner, current to the motor H, which operates the blower I2 and the fuel pump i3, is interrupted and their operation ceases. However, sufficient heat normally remains in the combustion chamber .to keep the thermostat-electrode 24 in expanded condition for a short period of time and this prevents the ignition switch 28 from tilting back to its original position to make" a circuit across the contacts 36 and 31. It is during this time of high temperature that fuel discharged into the combustion chamber is most hazardous.

It will also be apparent that upon openingof the main switch 13, either manually or automatically, the relay 21 is deenergized and this relay cannot be re-energized until the ignition control switchi28 is permitted to close by cooling and contraction of the thermostat-electrode 24. Thus,-with the switches 10 and 28 open and with the thermostat-electrode 24 in a hot condition, it is impossible to complete the ignition circuit and it is also impossible to inject fuel into the hot chamber i5 through the injector nozzle l6, because the relay 21 cannot be energized so long as the ignition switch 28 is open. Should the main switch l0 be closed at this time, the circuit to the motor I i will be completed and the blower i2 and fuel pump 13 will be started. Fuel will be by-passed in the pump 13 without reaching the burner nozzle l6 and the blower12 will blow airithrough the air chamber l5and combustion chamber 15* to cool the same and remove any explosive mixtures that may remain therein. Simultaneously, the incoming air will pass through the holes H in the push rod 49 to aid inoeffecting cooling of the thermostat-electrode 24 toatmospheric temperature. The contraction of the thermostat-electrode 24 will relieve the force acting upon the push rod 49 and thus permit the fuel control switch 29 to break. Thereafter, and upon further cooling of the thermostat-electrode 24, the ignition control switch 28 will be permitted to make and energize the relay 21 and complete theignition circuit. The spark produced thereby, of course, will again heat the thermostat-electrode 24, which again automatically causes the ignition switch 28 to open or break and the fuel control switch 28 to close or make and operate the solenoidevalve l3 controlling the supply of fuel to the burner nozzle it. If the spark fails or is of insuificient intensity to ignite the fuel, it will be insufiicient to actuate the thermostat-electrode 24 so that no fuel will be supplied to the burner, as has been previously explained.

Figure 3 illustrates a portion of a system such as shown in Figure l, modifying the same by the addition of a conventional pressure responsive switch P in the fuel line I1 between the pump 13 and the solenoid valve I 8. The switch P is arranged to complete the circuit through the conductors 3i! and 32 so long as a predetermined pressure exists in the line 11. Opening of the solenoid fuel control valve ill, of course, does not relieve the pressure on the switch P so as to permit the same to open because the burner nozzle' I5 maintains a sufficiently high back pressure to keep said switch closed while the burner is in operation.

The switch P adds a further safety feature to the invention in that should there be a momentary lack of fuel in the line I? or should the supply of fuel become exhausted, the current to the system normally flowing through the conductors 3G and 32 will be discontinued. The valve IE will then automatically close, the spark between the electrodes 20 and 34 will beinterrupted, the signal lamp 45 will go out, etc.

If the fuel failure is only momentary, and pressure in the fuel line is quickly built up, nevertheless the resumption of the operation of the burner will be the same as from a cold-start condition. That is to say, although the circuit is again completed by the switch P through the conductors 30 and 32, no fuel can be supplied to the nozzle I6 unless the spark at the electrodes 20 and 24 is of sufiicient intensity to assure ignition of the fuel. The system then operates in the manner aforedescribed.

When the system including the pressure responsive switch P is put out of operation automatically or manually by opening of the main switch iii, sufiicient pressure will be maintained in the line H to keep its contacts closed so that the electrical connection itself across the conductors 3B and 32 is not interrupted, although no current reaches these conductors at that time due to opening of the switch iii. Hence, when the main switch It! is again closed the current to the system is completed and no delay occurs in the starting up of the burner.

It will be clear from the foregoing that the present control system provides for a maximum of safety in that it absolutely prevents initiation of the supply of fuel to the burner nozzle at such times as would present a danger from fire or explosion. A11 danger from restarts is avoided by provid ng for a predetermined time delay and cooling before ignition can again occur, such gases as may have remained in the combustion chamber being scavenged during this cooling period so that when ignition does occur it precedes the introduction of fresh fuel into the fire box or combustion chamber and the spark must be of such intensity as to be capable of igniting the fuel before such fuel can be introduced.

In the system above described the spark is maintained throughout the operating period of the burner, but if desired the system can be modified to discontinue the ignition after a flame has been established in the fire box 15 This may be accomplished by adjusting the relative compression of the springs 63 and 86 associated with the switches 28 and 25! so that the ignition control switch 28 is opened by heating of the thermostat-electrode 2 by the heat of the burning fuel after the fuel control switch 29 has been closed due to heating of the thermostat-electrode 2G by the ignition spark. Further, a suitable lost motion connection (not shown) is provided so that upon cooling of the thermostat-electrode 24, the ignition switch 28 is closed after the fuel control switch 29 has been opened. The circuit must be slightly altered by connecting the primary coil 22 of the ignition transformer 22, as shown in Figure 3, so that the ignition spark is discontinued whenever the ignition switch 28 is open. Thus, the primary coil 22 of the ignition transformer 22 is placed in series with the ignition control switch 28, the circuit being traced from line 8, Figure 1, through conductors 32, 33' and 39, across contacts 35-3! of the ignition switch 28, conductor 38, and conductor "f2 (Figure 3) to the primary coil 22b, conductor 33 (Figure 1),

contacts R and R of relay 2'! and conductors 3i and 30 to the other side of the line 9. Upon opening of the main switch in to de-energize the relay 2? ignition cannot be reestablished until the thermostat-electrode 24 has cooled sufficiently to first open the fuel control switch 23 and then close the ignition switch 28. When this has occurred the operation is the same as described with respect to Figure 1 until continued heating of the thermostat-electrode 24 due to a flame heat causes opening of the ignition switch 28 to discontinue the ignition.

While the switches 28 and 29 have been described as mercury switches it is to be understood that the invention contemplates the use of snap action switches, micro-switches, or any other switches capable of functioning in the system to accomplish the objectives of the invention.

It will be understood that various other changes may be made in the control system disclosed herein. For example, a time delay switch may be used in place of the relay switch and this would insure a definite time after the blower has been turned on, or the main switch closed, before the fuel could be supplied to the burner. Again, a motor driving the fuel pump could be substituted in place of the solenoid valve, or this motor could also drive the blower and could be started through the same circuit that actuates the solenoid valve. The latter arrangement, of course, would have the distinct disadvantage of increasing the cooling down time and eliminating the free blower time to expel combustible gases that may have accumulated in the combustion chamber.

It will also be understood that while the ignition switch 28 and the fuel control switch 29 have been described as actuated upon expansion of the thermostat electrode 24, these switches can obviously be arranged for actuation upon icontractive movement of the thermostat-elecrode.

It is conceivable that still further specific changes may be made in the system without departing from the spirit of the invention or the scope of the appended claims.

I claim:

1. A fuel burner control system comprising: a burner; valve means for controlling the flow of fuel to said burner; continuously operating means for supplying air to said burner and for supplying fuel under pressure to said valve means; means for igniting said fuel, said ignit ng means comprising an ignition circuit including a source of high volta e current and a pair of spaced current conducting electrodes, one of said electrodes being connected to said source of high voltage current and the other of said electrodes being grounded and being thermally reactive to change its shape in response to the heat of the spark produced between said electrodes; and means controlled by said thermally responsive electrode operable to cause said fuel flow controlling valve means to permit a flow of fuel to said burner only when said thermally responsive electrode is expanded by the heat of a spark of sufficient intensity to ignite said fuel.

2. A fuel burner control system comprising: a burner; a fuel pump; a circuit including electrically operated valve means for controlling the flow of fuel from said pump to said burner; means for igniting said fuel, said igniting means including an ignition circuit having a pair of spaced current conducting electrodes connected therein, one of said electrodes being bimetallic and adapted to change its shape in response. to the heat of the spark produced between said electrodes; a motor for driving said fuel pump connected to be driven simultaneously with the initiation of the spark; and a switch in the circuit of said flow controlling valve means actuable to its closed position by said bi-metallic electrode to effect opening of said valve means when said bi-metallic electrode is subjected tov the heat of a spark of sufficient intensity to ignite said fuel.

3. A fuel burner control system comprising: a burner; a fuel control circuit including an electromagnetic valve for controlling the flow of fuel to said burner; continuously operating means for supplying air to said burner and for supplying fuel under pressure to said electromagnetic valve; means for igniting said fuel, said igniting means comprising an ignition circuit including a source of high voltage current and a pair of spaced current conducting electrodes connected in said circuit, one of said electrodes. being bimetallic and adapted to change its shape in response to the heat of the spark produced between said electrodes; and a switch in said fuel circuit controlled by said heat responsive electrode operable to efiect opening of said electromagnetic valve to permit a flow of fuel to said burner when said heat responsive electrode is subjected to the heat of a spark of sufiicient intensit to ignite said fuel.

i. A fuel burner control system comprising: a burner; a fuel supply control circuit including means for controlling the supply of fuel to said burner; means for igniting said fuel, said igniting means comprising an ignition circuit including an ignition transformer, and a pair of spaced current conducting electrodes connected in said circuit positioned adjacent said burner, one of said electrodes being thermally reactive to change its shape in response to the heat of the spark produced between said electrodes; and means including a pair of switches actuable by said thermally responsive electrode solely as a result of spark-heating thereof, one of said switches being arranged in saidfuel. supply control circuit to complete the circuit to said fuel flow control means to permit fuel to flow to said burner when said thermally responsive electrode is subjected to the heat of a spark of sufficient intensity to ignite said fuel, and the other of said switches being connected in circuit with said electrodes and being arranged so that it must be closed at the start of ignition and to open after said. fuel, has been ignited.

5. A fuel burner control system comprising: a burner; a circuit including, a main switch; a motor in said circuit; a blower, said motor being connected to drive said blower immediately upon closing of said main switch; a fuel circuit including electrically operated means for controlling the supply of fuel to said burner; means for igniting said fuel including an ignition circuit connected to be completed upon closing of said main switch and having a pair of spaced current conducting electrodes connected therein, one of said electrodes being thermally reactive and in,- cluding a portion movable as a result of being heated by the spark produced between said electrodes; and a fuel control switch in the circuit of said electrically operated means arranged to be closed upon movement of said movable portion of said one electrode when said one electrode is subjected to the heat of a spark of sufficient intensity to ignite said fuel.

6. A burner control system comprising; a burner; a circuit including electrically operated means for supplying fuel to said burner; fuel ignition means including an ignition circuit having an ignition switch and a pair of current conducting electrodes connected therein positioned adjacent said burner, one of said electrodes comprising a bi-metallic strip; means operable upon expansion of said bi-metallic strip as the result of spark-heating thereof for actuating an ignition control switch and a fuel control switch; and an ignition switch in said ignition circuit and a fuel control switch in said first-mentioned circuit arranged to be actuated by said last-mentioned means, said ignition switch being closed and said fuel switch being open when said bi-metallic strip i cool.

7. A burner control system comprising: a burner; a circuit including electrically operated means for supplying fuel to said burner; fuel ignition means including an ignition circuit having a pair of current conducting electrodes connected therein and positioned adjacent said burner, one of said electrodes comprising a bimetallic strip; means operatively engaged with said bi-metallic strip and arranged for actuation by expansion and contraction of said bi-"netallic strip; and an ignition switch in said ignition circuit and a fuel control switch in said first-mentioned circuit arranged to be actuated by said last-mentioned means, said ignition switch being closed and said fuel switch being openwhen said bi-metallic strip is cool, said ignition switch and fuel switch being further arranged so that upon expansion of said lei-metallic strip as a result of spark-heating thereof said ignition switch is opened before said fuel switch is closed.

8. A burner control system comprising: a burner; a circuit including electrically operated means forsupplying fuel to said burner; fuel ignition means including an ignition circuit and a pair of electrodes connected in said circuit and positioned adjacent said burner nozzle, one of said electrodes comprising a b-i-metallic strip; means operatively engaged with said bii etallic strip and arranged for actuation by expansion of said pi-metallic strip; and an ignition switch connected in said ignition circuit and a fuel control switch connected in said first-mentioned circuit arranged to be actuated by said last-mentioned means, said ignition switch being closed and said fuel switch being open when said bimetallic strip is cool, and said ignition switch and fuel switch being arranged so that said fuel switch is closed before said ignition switch is opened when said bi-metallic strip is heated by a spark of sufficient intensity to ignite said fuel.

9. A burner control system comprising: a burner; an ignition circuit including a pair of electrodes positioned adjacent said burner, one of said electrodes being bi-metallic; continuously operating means for supplying air to said burner; a continuousiy driven fuel pump for supplying fuel to said burner nozzle; a conduit connecting said fuel pump with said burner; a fuel circuit having a solenoid valve connected therein and arranged in said conduit for controlling the supply of fuel to said burner; means operatively associated with said bi-metallic electrode and arranged to be actuated upon expansion of said =bimetallic electrode; and a fuel control switch connected in said fuel circuit arranged to be actuated by said last-mentioned means to effect opening of said valve upon actuation of the ignition bimetallic electrode when said spark between said- 13 electrodes is of an intensity sufficient to ignite the fuel.

0. A furnace and control system therefor comprising: an air inlet chamber; means for causing an air stream to flow through said air inlet chamber: a burner in said air inlet chamber: ignition means including a bl-metallic electrode having inner and outer surfaces positioned adjacent said burner; means shielding the inner surface of said lei-metallic electrode from the incoming air stream; a tube operatively associated with said bi-metallic electrode, said tube having one end thereof terminating adjacent the inner surface of said 'bi-metallic element and having a plurality of apertures extending through the wall thereof, said apertures being arranged in the path of the oncoming air stream so as to admit air into said tube for discharge through said one end of said tube adjacent the inner surface of said bi-metallic electrode to eifect cooling of said inner surface.

11. A safety control system for fuel burners comprising: a, burner; a circuit including electrically operated means for supplying fuel to said burner; ignition means including an ignition circuit having a pair of electrodes connected therein and arranged adjacent said burner for igniting said fuel: a relay and an ignition switch connected in circuit with said ignition means. said relay being arranged in the circuit so that one pair of its contacts is in parallel with the confacts of said ignition switch; a solenoid valve in said first-mentioned circuit for controlling the supply of fuel to said burner; and a fue control switch in said first-mentioned circuit arranged to control said solenoid valve; actuating means for said ignition switch and fuel control switch arranged so that upon the formation of spark of predetermined intensity between said electrodes said fuel control switch will be closed. to complete the circuit to said solenoid valve, and said ignition control switch will be opened.

12. Fuel burning apparatus comprising: a furnace having an air-intake vchamber and a fire box or combustion chamber above said air-intake chamber; a circuit including an electrically operated blower for introducing air into said chamberfa burner in said air-intake chamber; a conduit for supplying fuel to said burner; a fuel control circuit including an electrically controlled fuel valve connected in said conduit; an ignition circuit having a pair of electrodes connected therein and arranged adjacent said burner, said ignition circuit including a relay, an ignition transformer an ignition switch, said. ignition switch being connected in parallel with one pair of contacts of said relay; a fuel control switch in said fuel control circuit for controlling the operation of said electrically operated fuel valve; a main switch for controlling the supply of current to said blower, ignition and fuel circuits, said ignition switch being closed when said burner is in cold condition and said fuel control switch being open when said burner is in cold condition, said ignition switch and fuel control switch being arranged to be operated in succession in response to the formation of a spark of predetermined intensity between said electrodes; and means operated in accordance with the intensity of said spark arranged to first close said fuel control switch to effect opening of said electrically controlled valve to supply fuel to the burner and to thereafter open said ignition control switch.

13. A burner control system comprising: a burner; an ignition circuit having a pair of electrodes connected therein and positioned adjacent 14 said burner, one of said electrodes being thermally responsive; means in said ignition circuit for producing a spark at said electrodes; a fuel pump for supplying fuel to said burner nozzle; a conduit connecting said fuel pump with said burner;

a solenoid valve in said conduit for controllingthe supply of fuel to said burner; means operatively associated with aid thermally responsive electrode arranged to be actuated upon expansion of said thermally responsive electrode; means comprising a fuel control circuit including a switch arranged to effect opening of said solenoid valve upon actuation of said aforementioned means by said thermally responsive electrode when said spark between said electrodes is of an intensity sufiicient to ignite the fuel; and a pressure re sponsive switch in said fuel conduit between said fuel pump and said solenoid valve connected with said ignition and fuel control circuits arranged to interrupt the flow of current to said ignition and fuel control circuits upon a predetermined pressure drop in said fuel conduit.

14. A furnace and control system therefor comprising: an air inlet chamber; a blower arranged to introduce air into said air inlet chamber; a main switch controlling said blower; a burner in said air inlet chamber; a fuel switch; an ignition switch; a pair of electrodes positioned adjacent said burner. one of said electrodes being thermally actuatable to control said fuel and ignition switches in a given order; and means arranged to divert a portion of said incoming air to cool said thermally actuatable electrode, whereby if said main switch is closed at the time of fuel failure. said thermally actuatable electrode will be cooled and effect an opening of said fuel switch and closing of said ignition switch to condition the system for a restart.

15. A furnace and control system therefor comprising: an air inlet chamber; means for forcing air into said air inlet chamber; a burner in said air inlet chamber; spark ignition means including a thermally responsive electrode heated by said spark and positioned adjacent said burner; burner control means operable in accordance with the thermal condition of said thermally responsive electrode; means shielding said thermally responsive electrode from direct contact with said incoming air; and means for diverting a portion of said air to effect cooling of said electrode.

16. A furnace and control system therefor of the type described in claim 15, in which the means for diverting a portion of the incoming air to cool the thermally responsive electrode comprises a tube having an open end terminating adjacent said thermally responsive electrode and having a plurality of apertures extending through the wall thereof said apertures being arranged in the path of the incoming air so as to admit air into said tube for discharge through said open end adjacent said thermally responsive electrode to effect cooling of said electrode.

17. A burner control system comprising: a

burner; a fuel control circuit including electrically operated means for controlling the flow of fuel to said burner; an ignition circuit including means for continuously igniting said fuel, said igniting means including a pair of spaced current conducting electrodes, one of said electrodes being thermally responsive to the heat produced by the spark between said electrodes; an ignition switch arranged to be opened by said thermally responsive electrode solely as the result of sparkheating of said electrode; and a fuel control switch in the circuit of the electrically operated flow controlling means, means arranged to close and maintain said fuel control switch in closed position by the thermal reaction of said thermally responsive electrode only when said thermally responsive electrode is subjected to the heat of a spark. of sunicient intensity to ignite said fuel.

18. A burner control system, comprising: a

burner; means for supplying fuel to said burner; an ignition circuit comprising means for normally igniting said fuel including a thermally responsive electrode and an ignition switch in said ignition circuit, said ignition switch being actuatable by said thermally responsive electrode, said thermally responsive electrode being arranged to maintain said switch open to prevent the initiation of a spark when the first-named means is out of operation and said thermally responsive electrode is still in a heated condition; and means including a normally continuously operating motor driven blower arranged to quickly cool said thermally responsive electrode to atmospheric temperature to permit said ignition switch to close and complete the ignition circuit, whereby to condition the apparatus for automatic reinitiation of a spark.

19. A burner control system, comprising: a burner; means for supplying fuel to said burner; and means for spark-igniting said fuel including circuit means having an ignition switch and a pair of current conducting electrodes spaced apart and connected to normally maintain a continuous spark therebetween, one of said electrodes being bi-metallic and arranged to control said ignition switch to prevent the initiation of a spark when the burner is out of operation and said bimetallic electrode i still in a heated condition.

20. A burner control system, comprising: a burner; means including a switch for controlling the supply of fuel to said burner; and means for igniting said fuel including a circuit having an ignition switch and a pair of current conducting electrodes connected to produce a continuous spark between said electrodes at a point adjacent said burner, one of said electrodes being bimetallic and adapted to change its shape in response to heating by said spark and being arranged to control the switch of said fuel supply control means and said ignition switch to prevent the initiation of a spark and a subsequent supply of fuel to said burner when the burner is shut down and the bi-metallic electrode is still in a heated condition.

21. A control system for a fuel burner, comprising: a burner; means for supplying fuel to said burner; fuel ignition means including a circuit having a pair of current conducting electrodes connected to produce a spark adjacent said burner, one of said electrodes being bi-metallic; an ignition switch arranged in circuit with said electrodes, said ignition switch being operable by said bi-metallic electrode and being arranged so that it is opened when said bi-metallic electrode has been expanded a predetermined amount as the result of being heated by. said spark; and means including a normally continuously operating motor driven blower arranged to quickly effect cooling of said lei-metallic electrode when the burner is out of operation so that said bimetallic electrode will contract and allow said ignition switch to close to permit a restart.

22. Furnace control apparatus including a fire box; a burner operatively associated with said fire box; a normally continuously operating blower arranged to introduce air into said fire box; ignition means including circuit means having a'pair of current conducting electrodes con-- nected to produce a continuous spark adjacent said burner; an electric motor drivingly connected with said blower, said electric motor being connected in circuit with said ignition means so that it is placed in operation to effect scavenging of said fire box simultaneously with the initiation of said spark; and means controlled by one of' said electrodes for initiating and maintaining a supply of fuel tosaid burner upon spark-heating of said one electrode to a predetermined temperature;

23. A fuel burner control system, comprising: a burner; a, fuel supply circuit including electrically operated means for controlling the flow of fuel to said burner; means for igniting said fuel, said igniting means including ignition circuit means having a pair of spaced current conducting electrodes connected therein to maintain a continuous spark therebetween, one of said electrodes being a bi-metallio thermostat element and being adapted tochange its shape as a result of the heat produced by the spark between said electrodes; and a fuel control switch in the circuit of said electrically operated flow controlling means, said fuel control switch being arranged to be actuated to closed position by the change in shape of said bi-metallic thermostat element to allow fuel to be supplied to said burner only when said bi-metallic thermostat element is subjected to the heat of a spark of sufficient intensity to ignite said fuel.

2 A safety control system for fuel burners, comprising: a burner; means for supplying fuel to said burner; current conducting ignition electrodes adjacent said burner for igniting said fuel, one of said electrodes being bi-metallic and positioned relative tosaid burner so as to change its shape solely as a result of being heated by the spark; an ignition circuit forproviding a spark between said electrodes; an ignition switch in said ignition circuit; a fuel circuit including a fuel control switch for controlling said fuel supply means; and means actuatable in response to said change in shape of said bi-metallic electrode for actuating said ignition and fuel switches in succession and upon heating of said one electrode to a predetermined temperature solely by said spark.

25. A burner control system, comprising: a fuel burner; an ignition circuit including a pair of current conducting electrodes arranged adjacent said fuel burner, one of said electrodes being thermally responsive to the heat of the spark; a relay and a relay switch connected with said ignition circuit; an ignition switch connected in parallel with said relay switch; a main switch controlling the supply of current to said ignition circuit; a holding circuit including said relay switch for maintaining said relay energized when said main switch is closed and said ignition control switch is open; a fuel control circuit including an electrically operated valve for controlling the supply of fuel to said burner; a fuel control switch connected in said fuel control circuit for controlling said valve, said ignition switch and fuel control switch being arranged to be actuated upon predetermined expansion ofsaid thermally responsive electrode; and means actuated in accord-. ance with the thermal expansion of said thermally responsive electrode arranged to actuate at least said fuel control switch, whereby said electrically operated valve is opened when the spark between said electrodes reaches a predetermined intensity.

26. A burner control system, comprising: a burner; means for supplying fuel to said burner; an ignition circuit comprising means for continuously spark-igniting said fuel including a pair of current conducting electrodes, one of said electrodes being lei-metallic and of a generally verted U-shape and having one leg thereof fixed to a support and its other leg free to move in accordance with th heat produced solely by said spark, the other of said electrodes having its end 10 

